The present invention relates basically to the field of carburetion for internal combustion engines and more particularly to carburetors utilizing a variable venturi.
Most present automobile carburetors are designed with a fixed venturi to create a vacuum pressure in the induction duct in order to pull fuel from a fuel reservoir. The venturi, by its fixed nature, operates at a maximum efficiency over a small range of engine RPM. Furthermore, a different size venturi is generally required for different size engines in performance requirements. Seldom is an automobile operated in only the small range of speeds required for the maximum operational efficiency of the fixed venturi. Consequently, various complicated venturi arrangements including multiple venturi tubes have been included in carburetors in an attempt to make the carburetor more efficient over a wide range of operating conditions. A venturi is generally most ineffective at slow speeds in which the velocity of air through the induction duct is minimal. Special idle jets have been incorporated in carburetors in order to overcome this problem by passing additional fuel to the engine at low RPM. At higher RPM, the fuel from the special idle jet is not required and therefore provides a richer mixture than is needed for that particular RPM range. This results in loss of fuel in an over rich mixture of fuel to air. This loss is particularly notable at high speeds and during deceleration.
Other features have been added to carburetors to overcome the limitations noted with the fixed venturi type carburetor. One limitation is recognized when the carburetor is operating at low engine RPM. When the operator desires to quickly accelerate the automobile, quick depression of the throttle pedal causes the throttle valve to rapidly open. This allows for additional amounts of air to flow through the venturi before the vacuum pressure is increased to a higher RPM in order to draw additional fuel. Consequently, it is not infrequent that the engine will stall on the initial lean mixture. To overcome this limitation, accelerator fuel pumps have been incorporated in carburetors to operate in response to depression of the throttle pedal to pump additional fuel into the mixing chamber when the throttle is depressed rapidly. However, such a compromise results in a loss of fuel when the vehicle is traveling at high speeds and the accelerator pump is temporarily released and then depressed again. The pump adds the additional fuel to the engine which is wasted since the high air velocity through the venturi is sufficient to pull enough fuel into the cylinders to accomplish the objective without the necessity of the fuel pump.
It may be seen then that additional features added to existing fixed venturi carburetors frequently cause additional inefficiencies that balance with the limitations that they themselves introduce. All the above mentioned and further features attempt to compensate for the inefficiencies of the venturi over the full range of operating conditions and RPM. Ideally, the carburetor for an automobile should operate at high efficiency over the full range of engine operating RPM and load conditions.
Conventional air valve type carburetors have been utilized in an attempt to maintain a constant air velocity across a fuel jet orifice independent of the throttle valve position and engine speed. Such carburetors generally attempt to vary the size of the fuel jet in accordance with the amount of air entering the carburetor to therefore provide a correct "air-fuel ratio." Engines having such air valve carburetors are generally difficult to start and operate at idling RPM.
Each additional compensating feature added to existing carburetors over the years makes them more complicated and more susceptible to plugging and therefore necessitate more frequent repairs and maintenance adjustments. In addition, the number of moving parts in carburetors has increased substantially over the years making such carburetors extremely complicated and increasingly expensive to manufacture.
The principal reason that variable venturi carburetors have not been a success in the past is because proper metering of fuel at low speeds has been nearly impossible to maintain. With the engine running, a high vacuum is created in the manifold that is so great that prior variable venturi carburetors would deliver too much gasoline to the engine. The result is that the engine floods too easily or becomes very uneconomical to operate at low speed ranges.
It is therefore a primary object of this invention to provide a variable venturi carburetor that will effectively operate throughout the entire engine operation range from idle to full throttle RPM while maintaining a correct air-fuel mixture ratio throughout that range.
An additional object is to provide such a variable venturi carburetor wherein the fuel enters the mixing chamber at a point where the air is moving at an extremely high velocity to thereby thoroughly mix air and fuel prior to its reception by the engine combustion chambers.
An additional object is to provide such a variable venturi carburetor wherein fuel is delivered from a single fuel supply orifice throughout the entire operational range of the engine.
Another principal object of this invention is to provide a carburetor of very simple construction wherein very simple adjustments may be made to vary the fuel-air ratio.
A further object is to provide a single throat carburetor that will operate as efficiently as any presently known multiple throat carburetors.
A yet further object is to provide a variable venturi type carburetor that does not utilize an idle jet, an accelerator pump, a needle valve, or a butterfly type throttle valve.
An additional object is to provide such a carburetor that is adaptable to replace most conventional downdraft type carburetors.
These and still further objects and advantages will become apparent upon reading the following detailed description of a preferred embodiment.